Thermochemistry Calculator

Compute reaction enthalpies with Hess's law and calorimetry heat transfer — with step-by-step substitution arithmetic and energy-unit conversion.

Everything you need for thermochemistry problems

Hess's law calculator

Build reactions from tabulated ΔHf° values, standard-state elements, or custom compounds.

Calorimetry (q = mcΔT)

Enter mass, specific heat, and temperature change — with tabulated c values for common substances.

Substitution arithmetic

See the full Σ(ν ΔHf°) breakdown for products and reactants, not just the final answer.

Energy unit toggle

Switch results between J, kJ, cal, and kcal using the thermochemical calorie (4.184 J).

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Reference data from NIST-JANAF and CRC Handbook values at 298.15 K.